Flipping a function's argument order in Python

Question

Nowadays, I am starting to learn haskell, and while I do it, I try to implement some of the ideas I have learned from it in Python. But, I found this one challenging. You ca

Answer 1

In a pure functional style:

flip = lambda f: lambda *a: f(*reversed(a))

def divide(a, b):
    return a / b

print flip(divide)(3.0, 1.0)

A bit more interesting example:

unreplace = lambda s: flip(s.replace)

replacements = ['abc', 'XYZ']
a = 'abc123'
b = a.replace(*replacements)
print b
print unreplace(b)(*replacements) # or just flip(b.replace)(*replacements)

Answer 2

You can create a closure in Python using nested function definitions. This lets you create a new function that reverses the argument order and then calls the original function:

>>> from functools import wraps
>>> def flip(func):
        'Create a new function from the original with the arguments reversed'
        @wraps(func)
        def newfunc(*args):
            return func(*args[::-1])
        return newfunc

>>> def divide(a, b):
        return a / b

>>> new_divide = flip(divide)
>>> new_divide(30.0, 10.0)
0.3333333333333333